The present application claims priority to Japanese Patent Application No. 11-166844 filed Jun. 14, 1999, the entire content of which is hereby incorporated by reference.
1. Field of the Invention
The present invention pertains to a near field light generating device, and more particularly, to a device that generates near field light used for high-density recording onto an optical recording medium, or for reproduction from such a recording.
2. Description of the Related Art
In the area of optical memories in which information is optically recorded and reproduced, as computers become increasingly faster and more advanced multimedia formats are developed, an optical head that can record a larger amount of information, i.e., in which the recording density is markedly improved, is being sought. A near field light recording technology has been proposed as a technology to realize such an optical head. In a conventional optical memory using laser light, the upper limit of recording density is determined based on the diffraction limit of the light, and recording and reproduction are possible only of marks the size of the wavelength of the light (approximately several hundred nanometers). With an optical memory using the near field light phenomenon that has been proposed in recent years, an optical head comprising a probe that has a small opening smaller than the wavelength of the light or solid immersion lens is placed as close to the recording medium (optical disk) as several tens of nanometers, and recording/reproducing light is irradiated onto the recording medium. Consequently, marks as small as several tens of nanometers, beyond the diffraction limit of the light, may be written and read as signals.
The probe referred to above is made of a medium having a high refractive index and has a small opening, such that near field light may pass through this small opening. For example, Japanese Laid-Open Patent Application No. Hei 7-192280 discloses a fiber probe. However, when fiber is used, optical axis adjustment is necessary for the fiber and prism, which are located between the laser light source and the small opening, and because this adjustment is complex, the manufacturing cost increases. Moreover, this technology has the problem that the weight of the optical head itself increases, which translates into a longer access time.
A solid immersion lens technology is disclosed in U.S. Pat. No. 5,729,393. However, where a solid immersion lens is used, optical axis adjustment is also necessary for such things as the condenser lens and holder, which means that it has the same problem as the fiber probe.
On the other hand, U.S. Pat. No. 5,625,617 discloses a technology in which a concave area is formed on the light exit surface of the semiconductor laser through focus ion beam (FIB) treatment so that near field light may be generated from this concave area. However, since FIB treatment uses a high-energy ion beam, there is a possibility that the light exit surface, which also comprises a cleavage plane that plays an important role as a laser resonant surface, may be damaged, resulting in laser oscillation failure.
The object of the present invention is to provide a near field light generating device that has a simple construction and that does not require complex optical axis adjustment.
Another object of the present invention is to provide a near field light generating device that does not experience such problems as laser oscillation failure.
These and other objects are attained by a near field light generating device comprising: a light emitting element that emits light from its exit surface; and a thin film that is formed on the exit surface and gains a light transmitting property when irradiated with light from the light emitting element.
The objects described above are also attained by a near field light generating device comprising: a light emitting element that emits light from its exit surface; and a thin film that is formed on the exit surface and gains a light transmitting property when heated.
For the thin film mentioned above, inorganic materials or organic materials having a low melting point are used. If an inorganic material is used, it is preferred that the melting point be 350xc2x0 C. or less, and more preferably, that a metal material having a melting point of 150xc2x0 C. or lower be used. It is also preferred that a heat diffusion preventing film exist between the light exit surface and the thin film.
In the near field light generating device pertaining to the present invention, because the area of the thin film irradiated with the light emitted from the light exit surface is heated, it becomes amorphous and transforms into a small light transmitting area. This small light transmitting area functions in the same way as the small opening of the conventional probe, and allows the emitted light to escape as near field light. The irradiated area of the thin film returns to a crystalline state from an amorphous state when the light emission is stopped, thereby ensuring reproducibility.
In other words, the near field light generating device pertaining to the present invention has an extremely simple construction, comprising only a light emitting element and a thin film formed on the light exit surface of the light emitting element, making it compact in size and lightweight. Therefore, the near field light generating device pertaining to the present invention is quite suitable for a near field light optical head.
In addition, because a small light transmitting area that generates near field light is formed in the thin film by means of the light emitted from the light emitting element, the complex process of aligning the optical axes of multiple components is not necessary. The near field light generating device pertaining to the present invention may also be mass-produced using ordinary semiconductor manufacturing technology. Therefore, it may be manufactured at a low cost.
In particular, it is preferred that a semiconductor laser be used as the light source. A semiconductor laser is small in size and lightweight, and is best suited for the near field light generating device in today""s market. Further, the present invention does not use a high-energy focus ion beam, and therefore the possibility of damage to the laser""s cleavage plane and resulting oscillation failure is eliminated.
The invention itself, together with further objects and attendant advantages, will best be understood by reference to the following detailed description taken in conjunction with the accompanying drawings.